Thermoplastic olefins (“TPO”) are polymer blends having a combination of both elastic and thermoplastic properties. They exhibit some of the properties of a cured elastomer as well as the reprocessability of thermoplastic resins. The elastomeric characteristics may be enhanced if one component of the blend is a vulcanizable elastomer which is wholly or partially crosslinked.
U.S. Pat. No. 4,130,534 discloses elastoplastic compositions comprising a blend of a thermoplastic crystalline polyolefin resin and a rubber which may be butyl rubber, chlorobutyl rubber or bromobutyl rubber. U.S. Pat. No. 4,639,487 discloses a heat shrinkable thermoplastic composition of an ethylene copolymer resin with a dynamically vulcanized halogenated butyl rubber. U.S. Pat. No. 6,013,727 discloses a blend of thermoplastic resin with a halogenated copolymer of a C4 to C7 isomonoolefin and a para-alkylstyrene.
U.S. Pat. No. 4,172,859 discloses a thermoplastic composition containing a polyamide matrix resin and at least one polymer having a specified tensile modulus. U.S. Pat. No. 4,174,358 discloses a thermoplastic composition containing a polyamide matrix resin and at least one polymer having a specified tensile modulus.
The earliest work in the curing of TPO compositions was by Gessler and Haslett, such as in U.S. Pat. No. 3,037,954, which teaches the concept of “dynamic curing,” wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer cured while continuously mixing and shearing the polymer blend. The result is a micro-gel dispersion of cured rubber in an uncured matrix of resinous thermoplastic polymer. U.S. Pat. No. 3,037,954 discloses compositions comprising polypropylene and a rubber wherein the rubber may be, butyl rubber, chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutene. Compositions of about 50 to 95 parts polypropylene and about 5 to 50 parts of rubber are disclosed.
Dynamically vulcanized thermoplastic compositions comprising a polyamide and various types of elastomers are known. See, for example, U.S. Pat. No. 4,173,556; U.S. Pat. No. 4,197,379; U.S. Pat. No. 4,207,404; U.S. Pat. No. 4,297,453; U.S. Pat. No. 4,338,413; U.S. Pat. No. 4,348,502; and U.S. Pat. No. 4,419,499. U.S. Pat. No. 4,287,324 discloses a dynamically vulcanized composition comprising a blend of crystalline polyester and a cured epichlorohydrin. U.S. Pat. No. 4,226,953 discloses a dynamically vulcanized composition comprising a blend of styrene-acrylonitrile resin and a nitrile rubber. U.S. Pat. No. 4,350,794 discloses a polyamide molding and extrusion composition prepared by melt blending a polyamide resin and a polyamide reactive halogen functional elastomer.
EP722850B1 (and related U.S. Pat. No. 6,079,465, U.S. Pat. No. 6,334,919) disclose a low-permeability thermoplastic elastomer composition useful as a gas-barrier layer in pneumatic tires. The composition comprises a thermoplastic matrix, such as polyamides or blends of polyamides, in which a low-permeability rubber, such as brominated poly(isobutylene-co-paramethylstyrene) (BIMS) is dispersed. EP857761A1 (related US Patents include U.S. Pat. No. 5,910,544; U.S. Pat. No. 6,062,283; U.S. Pat. No. 6,397,912) and EP969039A1 (related US Patents include U.S. Pat. No. 6,359,071; U.S. Pat. No. 6,538,066; U.S. Pat. No. 6,861,470) limit the viscosity ratio between the thermoplastic matrix and the rubber dispersion to achieve phase continuity in thermoplastic and fine rubber dispersions. EP969039A1 also discusses the relationship between the rubber dispersions and durability of the thermoplastic elastomer composition.
There is still a need to improve the properties of uncured and of dynamically vulcanized alloys.